I believe those are called "sniffer" rooms. They call the apparatus at the top an "electronic nose" as it is an explosives detection sensor. The air is measured/calibrated, then pushed up past you in the chamber in a burst, then concentrated rapidly and measured again. The result is compared to the initial sample and checked for any fumes from explosives that may have been introduced.

My question is; what would happen if you inadvertently introduced a high concentration of natural methane gas while in the chamber?